The present invention relates generally to the field of fluid containment systems for controlling over-pressure conditions in a refrigerant evaporator of a mechanical refrigeration system. More particularly, in the preferred embodiment the present invention relates to a low pressure centrifugal chiller having the refrigerant evaporator in fluid communication with a containment vessel for receiving refrigerant fluid from the over-pressure evaporator.
A low pressure centrifugal chiller is generally utilized in commercial and industrial refrigeration systems, such as for providing air conditioning in hotels, cooling fluid for a manufacturing process, and commercial food refrigeration systems. Low pressure centrifugal chillers typically use a chlorinated fluorocarbon (CFC) refrigerant in their operation. CFC refrigerants, many of which are sold by DuPont under the well known tradename FREON, have various boiling points, depending on the particular type of CFC refrigerant. Some typical types of CFC refrigerants are for example, R11, R113 and R123. FREON and its related family of compounds are well known and widely used as heat transfer media in mechanical refrigeration systems.
Mechanical refrigeration systems generally utilize the evaporation of liquid refrigerant into refrigerant vapor inside of the evaporator to absorb substantially large quantities of energy from a cooling fluid. The refrigerant vapor is then pumped to a refrigerant condenser where the latent heat of the pressurized vapor is removed, thereby condensing the vapor into a liquid. The above described cycle is repeated with the refrigerant liquid being vaporized in the evaporator and then subsequently condensed in the condenser.
The refrigerant evaporator generally contains a quantity of relatively low pressure refrigerant vapor. Under certain conditions the pressure within the evaporator can reach unacceptably high values. For example, in one type of cooling system, water is passed through the evaporator coils of a refrigeration system in order to be cooled, and the cooled water is then circulated through a water circulation system to other areas remote from the coils. In this cooling system the refrigeration system can be shut down while the water circulation system is left functioning. Therefore as the building or system warms the temperature of the circulating water-increases, thereby causing a temperature increase in the evaporator and vaporization of the refrigerant fluid within the evaporator, which raises the evaporator pressure.
Another type of temperature control system utilizes a common heat transfer fluid and circulation system to provide the heating and cooling for a structure. The system generally includes valves to divert the heat transfer fluid within the circulation system to either the refrigeration system or the boiler system. Valve misfunction or operator error can introduce hot heat transfer fluid from the heating system into the refrigeration system evaporator. The hot heat transfer fluid can cause rapid evaporation of the refrigerant within the evaporator, resulting in an evaporator over-pressure condition.
For many years it was an industry practice to include on the evaporator a safety relief valve to protect the equipment from an over-pressure condition; after the pressure in the evaporator exceeds a predetermined value the safety relief valve opens to release refrigerant gas into the atmosphere in order to lower the pressure buildup within the evaporator. Further, many mechanical refrigerant systems utilize a rupture disk that fragments or bursts into pieces at a predetermined pressure and allows the escape of refrigerant gas from the evaporator.
The release of refrigerant gas into the atmosphere while being an effective way to reduce evaporator pressure and save the equipment, unfortunately may contribute to pollution in the atmosphere. Most recently the United States and many other countries have agreed to halt the production of CFC refrigerants after 1995. Environmental concerns, though significant are not the only factor in favor of preventing the release of CFC refrigerant into the atmosphere. The refrigerant vented into the atmosphere is not recoverable and replacement refrigerant must be added to the system after the over-pressure condition is stabilized. In recent years the cost of CFC refrigerant has escalated drastically, having increased over tenfold for some refrigerant in the past years. Further, refrigerant vapor can displace the oxygen in an enclosed area and cause injury or death to persons or animals occupying the area. For these reasons it is desirable to ensure that no significant quantity of CFC refrigerant is vented into the atmosphere by the pressure relief system.
Many prior designers of mechanical refrigeration fluid systems have utilized a containment vessel to receive refrigerant fluid from an evaporator in order to reduce the ever-pressure condition in the evaporator. These prior fluid containment systems have utilized a valve, pump, or other auxiliary device to allow the transfer of refrigerant fluid from the evaporator to the containment vessel. A common limitation of the prior designs is the requirement of an auxiliary apparatus to facilitate the transfer of refrigerant fluid from the evaporator to the containment vessel. If the auxiliary apparatus fails to function, the evaporator will continue the over-pressure buildup which can result in the venting of refrigerant fluid into the atmosphere. Another limitation of the prior art systems is that these fluid containment systems only provides for the flow of refrigerant in one direction from the evaporator to the containment vessel, and not for a bi-directional flow of fluid. Therefore in the prior systems after the over-pressure condition has been stabilized it is necessary to perform additional functions to return the refrigerant fluid to the evaporator.
There remains a need for a fluid containment system for minimizing or preventing the venting of refrigerant gas from an over-pressure evaporator into the atmosphere. The present invention satisfies this need in a novel and unobvious way.